International Concrete Abstracts Portal

A common challenge in reinforced concrete construction is the need to connect bars of finite length to provide reinforcement continuity. Lap and mechanical splices are common methods that have been used to make continuous reinforcement. Lap splicing may cause additional congestion making concrete consolidation difficult. Mechanical splices are used when lap splicing is not practical. Different types of mechanical splices are commercially available for steel bars. For the case of GFRP reinforcement, mechanical splices are very useful in staged construction because the reinforcement cannot either be bent at the site or there is insufficient space for lap splicing. Mechanical splices for GFRP bars, however, must account for the low transverse stiffness and strength of the bars. For these reasons, only certain mechanical splices are practical for GFRP bars and careful consideration must be given to their installation and effectiveness. In this study, a commercially available swaged coupler was selected to investigate the behavior of spliced GFRP bars. Expected performance was numerically evaluated using a Finite Element (FE) model to develop a framework for test validation. The FE model was calibrated with a laboratory test to compare the results. The coupler’s length, the bar’s tensile strength, and the slip between the coupler and the bar were investigated. The outcome of this study allows for the definition of an efficient test campaign.

The goal of this study was to implement cost-effective techniques for improving bridge deck service life through the reduction of cracking. Work was performed both in the laboratory and in the field, resulting in the creation of Low-Cracking High-Performance Concrete (LC-HPC) specifications that minimize cracking through the use of low slump, low paste content, moderate compressive strength, concrete temperature control, good consolidation, minimum finishing, and extended curing. This paper documents the performance of 17 decks constructed with LC-HPC specifications and 13 matching control bridge decks based on crack surveys. The LCHPC bridge decks exhibit less cracking than the matching control decks in the vast majority of cases. Only two LCHPC bridge decks have higher overall crack densities than their control decks, which are the two best performing control decks in the program, and the differences are small. The majority of the cracks are transverse and run parallel to the top layer of the deck reinforcement. The results of this study demonstrate the positive effects of reduced cement paste contents, concrete temperature control, limitations on or de-emphasis of maximum concrete compressive strength, limitations on maximum slump, the use of good consolidation, minimizing finishing operations, and application of curing shortly after finishing and for an extended time on minimizing cracking in bridge decks.

When preparing ready-mix concrete for private applications, it is typically recommended that owners and contractors collaborate with suppliers and concrete specialists to understand the possibilities and limitations of concrete in their applications. Here, we describe a situation in which a homeowner took direct control over the exact specifications of concrete and admixtures, and ultimately resulted in an unsatisfactory concrete slab. The owner subsequently sued and settled with the concrete supplier outside of the court, which raises important questions regarding who maintains responsibility for concrete mixtures, their installation, and the final slab results. Suggestions are provided to help mitigate this problem.

Self-consolidating concrete (SCC), as defined by ACI 237R-07, is a very flowable, non-segregating concrete that can spread into placed, fill the formwork and encapsulate the reinforcement without any mechanical consolidation. SCC, compared to traditional concrete mixtures, has primary benefits that include a reduction in equipment and labor associated costs as well as higher construction effectiveness. Innovative materials such as high volume fly ash concrete (HVFAC), represent a substantial advantage to producing stronger, more durable cast-in-place (CIP) concrete members. A level of 50% fly ash to cement proportion, as well as both normal strength self-consolidating concrete (NS-SCC) and high strength self-consolidating concrete (HS-SCC), were employed in the implementation project for Missouri Bridge A7957. The objective of this research was to provide an implementation test bed and showcase for the use of these materials. The serviceability and structural performance, both short-term and long-term, of the concrete members within the bridge were monitored in an effort to investigate the in-situ performance of not only SCC but also HVFAC. The initial instrumentation program consisted of obtaining the temperature, strain, and deflection data for the different components within the bridge’s structure, from casting through service conditions. The results obtained from this two-year monitoring program will lead to propose certain specification requirements that can be used for future project implementations.

In recent years, it has been pointed out that many concrete structures are likely to accrue the initial defects in construction work because of the massive and complicated configuration and function of concrete structures. The service life of concrete structures and the structural performance will be lowered due to loading and environmental attack such as carbonation, frost action, and drying shrinkage. In the last few decades, various types of chemical admixtures have been developed, with emphasis on making highly durable concrete and on producing highly flowable concrete for self-compacting. In this paper, a new cement dispersing agent for retempering, denoted as CDA was examined to confirm its effect on fundamental properties of concrete. This chemical agent is used not only to improve the performance on vibrating consolidation of fresh concrete, but also to increase the resistance to segregation of concrete. The addition of agent will promise the dispersion of cement particles and the reduction of bleeding of concrete. The CDA is a negative ion type cement dispersing agent having a main component of Polyester fiber. The benefit of CDA is given in the dosage of a small amount of agent (0.5~1.0g/m3). The improvement in vibrating consolidation of fresh concrete was depended on late addition for retmpering. It was observed by the vibrating table-type consistency meter. From the tests for bleeding, setting, mechanical properties, durability, and micro structures of concrete such as Vickers hardness and pore size distribution, the benefit of CDA was also confirmed.